1. Field of the Invention
The present invention generally relates to a light-conductive circuit unit. More particularly, the invention relates to a light-conductive circuit unit adapted for use in optical transmission systems of a multiplex type to be installed in vehicles.
2. Description of Relevant Art
As an implement for transmitting a set of signals for controlling various electrical loads such as an audio device equipped in a vehicle, a variety of signal transmission systems of the optical type; which transmits an optical signal instead of electrical signal, have been proposed in recent years.
In those optical signal transmission systems, there were employed a variety of types of light-conductive circuits including a light-conductive member such as an optical fiber for transmitting a beam of light from a light source, and an optical switch provided in a light-conductive route of the light-conductive member. The optical switch is adapted to selectively transmit and interrupt the light beam from the light source to thereby produce an optical signal.
Among those optical transmission systems, there were found a number of multiple transmission systems of a multi-wavelength type in which the light beam as generated at the light source consisted of rays of light having a plurality of predetermined, different wavelengths. In those multiple transmission systems, the light-conductive circuit was such that the number of optical switches needed to be provided was equal to the number of the different wavelengths of the rays of light from the light source, which switches were connected in series or parallel in the light-conductive route. Exemplarily, three optical switches were provided where the light beam as generated at the light source included three types of rays of light having difference wavelengths: red-colored, green-colored, and blue-colored.
As such a light-conductive circuit, there were two typical examples disclosed. One in Japanese Patent Application Lay-Open Print No. 56-8103, laid open on Jan. 27, 1981, and the other in Japanese Patent Application Lay-Open Print No. 56-149840, laid open on Nov. 19, 1981. Of the two examples, each had three different wavelengths in the beam of light from a light source: the former having disposed a set of three optical switches in a light-conductive route, connected together in series; the latter also having disposed a set of three optical switches in a light-conductive route, while connected together in parallel.
Incidentally, in comparison with signal transmission systems of the electrical type which transmit electrical signals, the optical signal transmission systems of the class described had many advantages; such as that these were hardly affected by external noises and also structurally simplified.
However, in the optical transmission systems of the multi-wavelength type described, the light-conductive circuit was necessarily constituted as a combination of a number of separated optical switch elements, a number of optical lines consisting of optical fibers, and a variety of elements for optical connection such as between the optical switch elements and the optical fibers as well as among the optical fibers, exemplarily, such as an optical lens and an optical branching filter.
As a result, the light-conductive circuits had a complicated fabrication process, particularly when many optical switches were provided.
Moreover, at the connection between such components, it was difficult to sufficiently prevent the leakage of light, thus resulting in the problem of reduction in the light transmission efficiency of the entirety of such transmission systems.
The present invention has been achieved to effectively overcome such problems of conventional light-conductive circuits in the optical signal transmission system of the class described.